Type of Document Master's Thesis Author Escobar, Jose Alejandro URN etd-38431826109623300 Title Stress and fatigue analysis of svi-tested camshaft lobes Degree Master of Science Department Materials Science and Engineering Advisory Committee
Advisor Name Title Kampe, Stephen L. Landgraf, Ronald W. Reynolds, William T. Jr. Hendricks, Robert W. Committee Chair Keywords
- fracture surfaces
- fatigue engine testing
- rolling contact stress
- fatigue life prediction
- grinding residual stress
- camshaft lobes
- thermal damage
Date of Defense 1996-11-08 Availability unrestricted Abstract Nondestructive evaluation techniques were
employed to fully characterize three 2.3L
camshafts tested in an engine simulator for an
equivalent of 100,000 miles. Optical
microscopy, acoustic microscopy (SAM),
and profilometry were used to characterize
wear and fatigue, crack depth, and surface
roughness, respectively. Results show
cracking to occur mainly in the opening ramp
of the most abusively ground cam lobes. No
clear evidence was found for subsurface
cracking at depths as great as 200 mm from
the lobe's surface. Profilometry results show
no evidence of any major tribological effect
due to the sliding friction of the follower.
Fractography studies show a difference
between fracture surfaces among the cracks
examined; straight cracks exhibit features
resembling fatigue propagation, while fracture
surfaces from pitted cracks show a more
brittle behavior. Small grinding cracks
(approximately 300 mm in length) were found
in the opening ramps of the most abusively
ground lobes prior to testing. Knoop and
Nanoindenter microhardness indicate a
near-surface rehardening for the most
abusively ground lobe (confirmed by
metallography), and temper burn for the
remaining lobes. X-ray residual stress results
made in the opening ramp of the tested lobes
show evidence of residual stress relaxation.
X-ray line width data as a function of depth
does not correlate with residual stress.
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